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JWST-STScI-000444


MIRI SRR


MIRI Operations Concept

Dr. Margaret Meixner Space Telescope Science Institute

November 4-5, 2003


MIRI European Consortium

Margaret Meixner 1



MIRI SRR


Operations Concept Document (OCD)
· The OCD describes how MIRI is to be used to achieve the science requirements. · The OCD flows requirements into the Functional Requirements Document (FRD) and feeds into the overall Mission Operations Concept Document (MOCD). · The OCD has been developed in parallel with requirements documents and instrument design since Phase A. · The OCD is under CCB.
MIRI Mission Assurance Documents JWST Level I Requirements JWST Level II Requirements JWST Science Requirements

MIRI Science Requirements Document MIRI Operational Concept

MIRI Functional Requirements Document

MIRI Interface Requirements Document

MIRI Specification

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Key Instrument Ops Concepts
· · · · · · · Single proposal generation & planning system for science and calibration program Event-driven, not absolute-time based, operations High level commands to spacecraft Interleaved instrument operations
­ Parallel instrument operations for calibration

8 hours/day 5 days/week shifts, after commissioning On-the-fly calibration on the ground Keep Instrument Ops Simple and Similar

November 4-5, 2003


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Margaret Meixner 3



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JWST Mission Architecture
Operations Start Here

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Observatory operations: built around two main processors
CTP controls spacecraft
· Assures spacecraft subsystems responds to ICDH requests properly Responds to ground commands for datadumps, uploads etc

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·

ICDH controls the science program
· · · Home of instrument ops (and the OPE) Responsible for inst. safety Requests services from the CTP for slews, acquisitions, etc

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Basic principles of MIRI's operations · Event Driven Þ If campaign mode, then MIRI needs to warm up on time scale of a slew, ~30 minutes. · No MIRI mechanism movements during exposures. · Data Processing
­ On JWST
· Average samples of pixels by MIRI FPE · Lossless (2x) compression by ICDH/FPAP

­ On Earth
· Calibration · Up-the-ramp fitting
­ Flux estimation ­ Cosmic ray removal

· Combining dithered images to remove
­ Detector defects (dead or hot pixels) ­ Gaps in short wavelength FPAs

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Detector Operations
ü All 3 MIRI SCAs will be
­ Read out in Multiaccum mode · FASTMode, frame time = 3 seconds · SLOWMode, frame time = 30 seconds ­ 2 SCAs for MIRI IFU will be read out synchronously ­ Parallel operations of IFU and Imager SCAs will be synchronous

ü Subarrays
­ Permit shorter exposures for bright objects, high backgrounds, long wavelengths ( > 15 µm) ­ Readout like FASTMode but subarray, frame times = 0.04 to 0.66 seconds

ü Reference pixels
­ Allow monitoring/correction of drifts in bias & dark current

ü Idle Mode
­ Prevents saturation ­ Continuously reset/clock/dump charge

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SCA Readout Strategy

FASTMode: nsamp=1 SLOWMode: nsamp=10 Always: nframe=1

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MIRI has four Science Modes

1. Photometric Imaging 3. Coronagraphy 2. Low Resolution Spectroscopy

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MIRI has four Science Modes

4. Integral Field Unit Spectroscopy

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MIRI Imager: Subarrays

·128â128 for IFU target locate ·256â256 for coronagraph fields ·512â512 for bright objects, long wavelengths


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Activity Lists for MIRI Science Modes

· ·

The OCD describes at a high level how each of the four science modes will be done. Activity lists including target locate procedures have been outlined for each of the modes:
­ ­ ­ ­ Imaging Low Resolution Spectroscopy Coronagraphy Integral Field Unit Spectroscopy

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MIRI Coronagraphy

1. 2. 3. 4.

5. 6.

Slew Guide Star Acq. Perform target locate procedures autonomously Select coronagraph mask and corresponding diaphragm and filter combination Exposure Repeat exposures as required

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MIRI Coronagraphy Target Locate Procedure:Triangulation

1. Select neutral density filter 2. Expose and calculate "centroid" 3. Offset (<20") to coronagraph sweetspot, 5" from center 4. Quad-cell to center on sweet spot

5. Repeat 3 & 4 for sweetspot #2 6. Repeat 3 & 4 for sweetspot #3 7. Using stored locations of sweetspots # 1,2,3 to solve for offset to center of mask with 5 mas error

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Instrument Calibration
· STScI will coordinate the development of an integrated calibration plan by all the instruments
­ ­ Commissioning = PI responsibility Post-commissioning = STScI responsibility

·

STScI benefits from HST experience
­ ­ Calibrations planned using the integrated planning tool Yearly cycles for calibration programs tied to TAC

·

Calibration data will come from 3 sources:
1) 2) 3) science data observations done in parallel with science observations observing time dedicated to calibration

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Calibration Modes 1. 2. 3. 4. 5. Dark Current Flat field calibration Wavelength calibration for the IFU spectrograph Wavelength Cal. For LRS Read Noise Calibration

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Data Volume, Rates and Communications
· Requirement allocations:
­ 10 MHz X-band, rate limited to 8 Mbps ­ Contacts limited to one ground station contact per day (8.25 hours) ­ Maximum 232 Gbits Engineering and compressed Science data

·

Highest data-rate science:
­ Broadband imaging at 25 µm
· Frame size: 1024 â 1032 â 16 bits = 16.9 Mbits · 3 sec per readout Þ 5.64 Mbps = 2.82 Mbps of compressed data · 24 hours Mission elasped time Þ 243 Gbits

· ·

Typical MIRI science has 3 to 200 seconds per readout MIRI is used a third of the time
­ NIRSPEC+NIRCAM+FGS Tunable Filters = the other two thirds

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Open Issues: 1. 2. Dewar for MIRI means we may turn MIRI off to conserve cryogens
- campaign modes needs to be studied as an option

Coronagraphic target acquisitions

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Summary ­ Operations Concept
· Concepts for operations of JWST & MIRI are well-developed for the current stage of JWST
­ STScI brings HST experience to JWST ­ MIRI OCD developed in parallel with requirements since Phase A ­ MIRI Operations Concept in concordance with JWST Mission Operations Concept ­ MIRI used for Science

·

Keep Instrument Ops Simple and Similar
­ NIRCam, NIRSPEC, FGS-tunable filter MIRI all used by the same astronomer ­ Science-driven ­ Event-driven

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Backup Slides

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MIRI capabilities: 5-27 µm Imager (5-27 µm):
· 1 1kâ1k Si:As Sensor Chip Assembly (SCA) · 0.11"/pixel · Imaging with filters
­ 112"â84" FOV

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Integral Field Unit (IFU) Spectrograph (5-27/28.3 µm):
· 2 1kâ1k SCAs · 4 IFUs
­ slice widths: 0.18" to 0.64" ­ FOVs: 3.6"â3.6" to 7.6"â7.6"

· Coronagraphy
­ 4 FOVs, ~28"â28"

· Low-resolution spectroscopy (5-10 µm, R~100)

· R~3000 spectroscopy
­ 12 gratings, 3 per IFU

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MIRI Coronagraphy Peakup: Procedure I, Iterative offsets

MIRI SRR


1. 2. 3.

4. 5.

Select neutral density filter Expose and calculate "centroid" Offset (<20") to coronagraph sweetspot, 0.5" from center Quad-cell to center on sweet spot Offset (0.5") to mask center

Note: Science exposure repeated from 3 different sweetspot locations to minimize persistence effects.

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Science drives Requirements
· Most of time on statistical studies of faint objects
­ Dithering and good calibration required to maximize S/N ­ Pointings last several hours to several weeks, typical ½ day

·

OpsCon optimized for bulk of the science program
­ Capabilities that are required infrequently can be less efficient without hurting overall efficiency
For example: · Þ dithers should be time-efficient · Þ coronagraphic target locates need not be time-efficient

November 4-5, 2003


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